JP2010048456A - Exhaust gas treatment apparatus and exhaust gas treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas treatment apparatus and an exhaust gas treatment method reducing cost for catalyst denitration and increasing exhaust heat recovery efficiency while preventing sulfuric acid corrosion. <P>SOLUTION: The exhaust gas treatment apparatus is provided with: a waste heat boiler 3 for recovering heat of exhaust gas discharged from a combustion furnace 1; a urea water spraying device 2A for spraying urea water to exhaust gas in a temperature region of 400-700°C by heat recovery by the waste heat boiler 3; a low-temperature heat recovery device 4 for further recovering heat from low-temperature exhaust gas with heat recovered by the waste heat boiler 3 and sprayed with urea water; a dust collecting facility 6 for collecting dust in the exhaust gas with heat recovered by the low-temperature heat recovery device 4; and a catalyst denitration tower 8 for performing catalyst denitration of the exhaust gas with dust removed therefrom by the dust collecting facility 6. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to an exhaust gas treatment apparatus and an exhaust gas treatment method, and more specifically, is used for incinerators for incinerating municipal waste, industrial waste, etc., gas combustion furnaces attached to gasification melting furnaces, power generation, hot water use, etc. The present invention relates to an exhaust gas treatment apparatus and an exhaust gas treatment method for chemically treating exhaust gas discharged from a combustion furnace such as a furnace of a combustion boiler.

Conventionally, for example, a non-catalytic denitration method and a catalytic denitration method are known as methods for removing nitrogen oxides (NO _x ) in exhaust gas discharged from a combustion furnace such as a waste incinerator.

  In the non-catalytic denitration method, nitrogen oxides are decomposed by spraying urea water in which urea is dissolved in water into the combustion chamber of the combustion furnace. The higher the temperature in the combustion chamber in which the urea water is sprayed, the higher the nitrogen oxide removal efficiency. Therefore, urea water is sprayed on the in-furnace region in the range of 750 to 950 ° C. In this case, nitrogen oxide removal efficiency of about 30% can be expected. Excess urea spraying causes ammonium chloride to be generated, generating purple smoke from the chimney.

  In the catalyst denitration method, nitrogen oxides in combustion exhaust gas are decomposed into nitrogen gas in the presence of ammonia on the catalyst surface. In the catalytic denitration method, a removal efficiency of about 95% can be expected. However, in addition to the fact that the catalyst is very expensive, it is necessary to vaporize ammonia and blow it upstream of the catalyst denitration tower. A storage tank for storage, equipment for vaporizing ammonia, and the like are required, and the constituent equipment becomes complicated and expensive.

  FIG. 3 is a schematic view showing a conventional waste incineration facility. The waste incinerator 1 is provided with a urea water storage tank 2 for spraying urea water in the furnace. Combustion exhaust gas generated in the waste incinerator 1 is recovered from exhaust heat by an economizer 4a which is a kind of boiler 3 and a low-temperature heat recovery unit 4, and then a temperature reducing tower 5, a bag filter 6 which is a kind of dust collector, It is emitted from the chimney 10 through the reheater 7, the catalyst denitration tower 8 constituting the catalyst denitration equipment, and the induction ventilator 9. The deaerator 11 removes oxygen and carbon dioxide dissolved in the water supplied to the boiler 3. The temperature reducing tower 5 lowers the temperature of the exhaust gas to the heat resistant temperature (250 ° C. or lower) of the filter cloth material of the bag filter 6. A dry exhaust gas treatment device 12 that sprays a special reaction aid together with slaked lime is installed in the flue before the bag filter 6 to prevent clogging of the filter cloth and promote neutralization of HCl and SOx. Further, an ammonia vaporizer 13 and an ammonia storage tank 14 are installed to send ammonia gas into the catalyst denitration tower 8. Since the catalyst of the catalyst denitration tower 8 is deteriorated by the deposition of dust, sulfur oxide (SOx), and alkali metal, the catalyst denitration tower 8 is installed on the downstream side of the bag filter 6 and the dry exhaust gas treatment apparatus. The reheater 7 raises the temperature of the combustion exhaust gas to a temperature at which a catalytic reaction is likely to occur.

Since catalyst denitration is expensive as described above, in order to reduce this cost, urea water is sprayed on the upper stage in the incinerator, ammonia is generated by hydrolysis of urea, and waste is generated by a part of the generated ammonia. A catalytic denitrification tower is caused by causing a non-catalytic reaction in the incinerator and then performing a catalytic denitration reaction in a catalytic denitration tower connected to the downstream side of the waste incinerator using unreacted ammonia in the waste incinerator. There has been proposed an exhaust gas denitration method that eliminates the need for ammonia injection at the inlet (Patent Document 1).
JP-A-6-269634

  However, ammonia is gradually oxidized and decomposed from around 600 ° C. to generate ammonia-derived nitrogen oxides, which are reported to generate up to about 1000 ° C. with a peak at 800 ° C. (Takahashi). Yasumitsu and 6 others "Application as a deodorizing and decomposing device for diesel engines by lean combustion method" Gifu Prefectural Insurance Environmental Research Institute, 2006, No. 14).

  In general, the temperature in a furnace such as a waste incinerator is 800 ° C or higher, so when urea water is sprayed into a high-temperature furnace, ammonia is not thermally decomposed, and denitration in a catalytic denitration tower installed downstream. May become insufficient.

  In addition, the amount of nitrogen oxides and sulfur oxides generated in the combustion exhaust gas varies depending on the nature of the waste and the furnace load, and the unreacted ammonia concentration in the waste incinerator cannot be controlled. Denitration may not be possible.

Further, in large facilities such as municipal waste incineration facilities, exhaust heat is often recovered by an exhaust heat recovery boiler. This type of exhaust heat recovery boiler is a combustion gas at the boiler outlet in order to increase heat recovery efficiency. Often, it is equipped with a low-temperature heat recovery unit that preheats the feed water that is sent to the boiler using the sensible heat. In order to improve the exhaust heat recovery efficiency of the exhaust heat recovery boiler, it is conceivable to lower the feed water temperature, but so-called sulfuric acid corrosion (low temperature corrosion) must be considered. The sulfuric acid corrosion is generated by the sulfur oxides sulfur content in waste occurs by burning (SO ₃₎ is sulfuric acid reacts with the moisture in the exhaust gas. Sulfur oxides produced by the combustion of waste is mostly SO _2, are slightly SO ₃ also includes, sulfuric acid dew point alone this SO ₃ is contained several ppm is 120 to 130 ° C.. For this reason, the feed water temperature to the exhaust heat recovery boiler is set to 140 ° C. or higher so that the feed pipe of a low-temperature heat recovery device such as an economizer is not affected by sulfuric acid corrosion. That is, in order to prevent low temperature corrosion that SO ₃ contained in the exhaust gas reacts with moisture in the exhaust gas to become sulfuric acid and corrodes the economizer water supply pipe etc., the feed water temperature to the exhaust heat recovery boiler is the sulfuric acid dew point temperature As a result, the exhaust heat recovery efficiency could not be increased.

  Accordingly, an object of the present invention is to provide an exhaust gas treatment apparatus and an exhaust gas treatment method capable of reducing the cost in catalyst denitration and performing stable denitration.

  It is another object of the present invention to provide an exhaust gas treatment apparatus and an exhaust gas treatment method that can improve exhaust heat recovery efficiency while preventing sulfuric acid corrosion.

  In order to achieve the above object, an exhaust gas treatment apparatus according to the present invention includes a gas cooling facility for cooling exhaust gas discharged from a combustion furnace, and urea water to exhaust gas in a temperature range of 400 to 700 ° C. by the gas cooling facility. A urea water spray device for spraying, a dust collection facility for collecting dust in exhaust gas sprayed with urea water, and a catalyst denitration facility for catalytic denitration of exhaust gas from which dust has been removed by the dust collection facility, It is characterized by having.

  Moreover, the exhaust gas treatment apparatus according to the present invention is a waste heat boiler that recovers heat of exhaust gas discharged from a combustion furnace, and urea water is added to exhaust gas in a temperature range of 400 to 700 ° C. by heat recovery by the exhaust heat boiler. A urea water spraying device for spraying, and a low-temperature heat recovery device for recovering heat from the low-temperature exhaust gas sprayed with urea water while being recovered by the exhaust heat boiler. In this case, it further includes a dust collection facility that collects dust in the exhaust gas heat-recovered by the low-temperature heat recovery unit, and a catalyst denitration facility that performs catalyst denitration of the exhaust gas from which the dust has been removed by the dust collection facility. It is preferable.

  Furthermore, a control unit for detecting the ammonia gas concentration in the exhaust gas at a downstream position of the urea water spray device, and a control for controlling the spray amount of the urea water by the urea water spray device based on the detection result of the detection unit It is preferable to further have a part.

  Moreover, the exhaust gas treatment method according to the present invention is a method for cooling an exhaust gas exhausted from a combustion furnace to 400 ° C. to 700 ° C. and spraying urea water onto the exhaust gas cooled to 400 to 700 ° C. And the concentration of nitrogen oxides in the exhaust gas is reduced by catalytic denitration of the exhaust gas with the generated ammonia gas.

Moreover, the exhaust gas treatment method according to the present invention is a method for cooling an exhaust gas containing sulfur oxides discharged from a combustion furnace to 400 ° C. to 700 ° C., spraying urea water on the exhaust gas cooled to 400 to 700 ° C. And sulfuric acid corrosion is prevented by neutralizing SO ₃ in the exhaust gas with the generated ammonia gas.

In the exhaust gas treatment method according to the present invention, exhaust gas discharged from a combustion furnace and containing nitrogen oxides and sulfur oxides is cooled to 400 ° C to 700 ° C, and urea water is sprayed on the exhaust gas cooled to 400 to 700 ° C. In this way, ammonia gas is generated, and sulfuric acid corrosion is prevented by neutralizing SO ₃ in the exhaust gas with the generated ammonia gas, and exhaust gas is catalytically denitrated with the ammonia gas remaining without reacting with SO _3. It is characterized by reducing the nitrogen oxide concentration in the exhaust gas.

  In the exhaust gas treatment method, it is preferable that the ammonia gas concentration in the exhaust gas sprayed with urea water is detected and the spray amount of urea water is controlled based on the detection result of the ammonia gas concentration.

  According to the present invention, ammonia gas is generated by blowing urea water into exhaust gas whose temperature has been lowered to 400 ° C. to 700 ° C. after being discharged from a furnace such as a waste incinerator. The ammonia gas hardly thermally decomposes in the range of 400 ° C to 600 ° C. Ammonia gas begins to thermally decompose gradually from around 600 ° C., but since the rate of thermal decomposition in the range of 600 ° C. to 700 ° C. is small, ammonia gas can be obtained with a high production rate. Therefore, stable catalyst denitration is possible in the catalyst denitration reaction.

The generated ammonia gas reacts with SO ₃ in the exhaust gas in a temperature range of 250 ° C. to 400 ° C. to generate ammonium sulfate when the sulfur oxide is contained in the exhaust gas. As a result, in an exhaust gas system equipped with an exhaust heat boiler and a low-temperature heat recovery device, SO _{3 in} the exhaust gas is significantly removed before reaching the low-temperature heat recovery device such as an economizer, and the sulfuric acid dew point temperature in the exhaust gas is lowered. Can do. The temperature of the exhaust gas is lowered to 250 ° C. to 400 ° C. due to heat recovery by the boiler and evaporation of urea water. Accordingly, as described above, SO ₃ in the exhaust gas is removed in this temperature range and the sulfuric acid dew point temperature is lowered. Therefore, the temperature in the low-temperature heat recovery device such as boiler feed water introduced into the economizer is set lower than 140 ° C. The collection capacity can be increased.

  Moreover, the temperature of the exhaust gas that has passed through the low-temperature heat recovery device can be reduced by lowering the temperature in the low-temperature heat recovery device such as boiler feed water introduced into the economizer, and thereby, the dust collector such as a bag filter can be reduced. It is possible to omit or reduce the size of the gas cooling tower installed for the purpose of protection.

Further, by catalytic denitration of the exhaust gas with SO ₃ in the exhaust gas and unreacted ammonia gas, installation of an ammonia vaporization device and an ammonia storage tank can be eliminated, and costs can be reduced.

Furthermore, by detecting the concentration of ammonia gas generated by the urea water spray and controlling the spray amount of the urea water, it becomes possible to stably supply ammonia gas at a desired concentration according to the catalyst amount of the catalyst denitrification tower, In addition, even if the amount of SO _X generated varies depending on the nature of the garbage, the furnace load, etc., SO ₃ can be removed reliably and the generation of excess ammonia gas can be prevented.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, in all drawings and all the embodiments including the conventional apparatus of FIG. 3, the same components are denoted by the same reference numerals. First, as a first embodiment of an exhaust gas treatment apparatus according to the present invention, a waste incineration facility including the exhaust gas treatment apparatus of the first embodiment will be described with reference to FIG.

  The waste incineration facility shown in FIG. 1 includes a waste incinerator 1, which is a kind of combustion furnace, a boiler 3, a low temperature heat recovery device 4, a deaerator 11, a dry exhaust gas treatment device 12, and a bag filter 6 which is a kind of dust collector. , A reheater 7, a catalyst denitration tower 8 constituting a catalyst denitration facility, an induction ventilator 9, a chimney 10 and the like are connected directly or via a flue or the like. The low-temperature heat recovery device 4 is a device that recovers the amount of heat of the exhaust gas emitted from the boiler 3, and includes an economizer 4a, a deaerator heater 4b, an air heater (not shown), and the like.

  The illustrated incinerator 1 is a stalker-type incinerator and includes a combustion chamber 1a in the furnace. An exhaust gas outlet 1b is provided in the upper part of the combustion chamber 1a, and the exhaust gas is attracted by the action of the induction ventilator 9 and flows along the dotted arrow in FIG.

  The boiler 3 shown in FIG. 1 is integrated with the waste incinerator 1 and includes a radiant heat transfer section, a drum 3a, a contact heat transfer section 3B composed of a water pipe 3b communicating with the drum 3a, and the like. A water tube boiler is illustrated. In the flue 20 extending from the exhaust gas outlet 1b of the garbage incinerator 1 to the contact heat transfer section 3B, a known radiant heat transfer section is formed by a water cooling wall using an evaporation pipe and fins (not shown).

  The inside of the waste incinerator 1 (combustion chamber 1a) is about 800 to 1000 ° C. The exhaust gas discharged from the waste incinerator 1 is deprived of heat in the boiler 3, and is about 700 ° C. near the entrance of the boiler 3, and is about 400 ° C. near the exit of the boiler 3.

  A urea water spray device 2A for spraying urea water into the exhaust gas is installed in a region where the exhaust gas is in the range of 400 to 700 ° C. The urea water spray device 2A includes a urea water storage tank 2a that stores urea water, a conduit 2b that guides urea water to a predetermined location by a pump (not shown), and a spray nozzle 2c that is attached to the tip of the conduit 2b. it can. One or a plurality of urea water spraying portions are provided in a region where the exhaust gas is in the range of 400 to 700 ° C.

  The urea water sprayed on the exhaust gas at 400 ° C. to 700 ° C. generates ammonia gas. Ammonia hardly thermally decomposes in the range of 400 ° C to 600 ° C. In addition, it gradually begins to thermally decompose from around 600 ° C. to generate nitrogen oxide, and nitrogen oxide is generated up to about 1000 ° C. with a peak at 800 ° C. Since the thermal decomposition of ammonia proceeds rapidly from around 700 ° C., ammonia gas can be obtained at a high production rate even when urea water is blown into the exhaust gas at 600 ° C. to 700 ° C. In addition, you may make it spray urea water on the exhaust gas of 400 to 600 degreeC.

The exhaust gas that has been deprived of heat by the boiler 3 and deprived of vaporization heat by the evaporation of urea water is cooled to about 250 to 400 ° C. Thus, the temperature of the exhaust gas that has passed through the boiler 3 decreases to 250 to 400 ° C. before reaching the low-temperature heat recovery unit 4. Then, the SO ₃ in the exhaust gas in the temperature range of 250 to 400 ° C., is generated ammonium sulfate by reaction with ammonia gas from the urea water, as a result, SO ₃ in the exhaust gas which causes acid dew point drops Decrease.

When urea water was not blown upstream of the boiler 3, the SO ₃ concentration near the inlet of the low-temperature heat recovery device 4 was 17 ppm (dry state), but when a certain amount of urea water was blown, the SO ₃ concentration Has been experimentally confirmed to be about 2% (dry state), and can reduce about 90% of SO ₃ .

The SO _X concentration in the exhaust gas is 100 ppm, the SO ₃ ratio (SO ₃ / (SO ₂ + SO ₃ )) is 3%, the SO ₃ removal rate by urea water spray is 90%, and the moisture content in the exhaust gas is 15 vol. %, The sulfuric acid dew point temperature is 110 ° C. Accordingly, the heat medium temperature of the low-temperature heat recovery device 4 such as the water supply temperature of the economizer 4a and the deaerator heater 4b can be lowered below 140 ° C., and the heat recovery capability can be improved as compared with the conventional case. Become.

  Further, the exhaust gas temperature in the vicinity of the outlet of the economizer 4a has been conventionally designed to be about 220 ° C. However, in the present invention, for example, the feed water temperature of the boiler 3 is controlled to 120 ° C. to transmit the economizer 4a. The exhaust gas temperature can be lowered to 170 ° C. by increasing the heat area. As a result, the temperature reducing tower (see reference numeral 5 in FIG. 3) for the purpose of protecting the bag filter 6 can be omitted as shown in FIG.

Furthermore, the ammonia gas derived from urea water that has not reacted with SO ₃ passes through the downstream bag filter 6 and can act as ammonia for use in the denitration reaction in the catalyst denitration tower 8. As a result, a set of ammonia supply devices such as an ammonia vaporization facility (see reference numeral 13 in FIG. 3) and an ammonia storage tank (see reference numeral 14 in FIG. 3) for supplying ammonia gas to the catalyst denitration tower 8 are not required as in the illustrated example. Or miniaturization is possible.

  Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 2 is a schematic view showing a waste incineration facility including the exhaust gas treatment apparatus of the second embodiment.

  The second embodiment includes a detection unit 21 for detecting the ammonia gas concentration in the exhaust gas, and a control unit 22 for controlling the spray amount of urea water by the urea water spray device 2A based on the detection result of the detection unit 21. These are different from the first embodiment, and other configurations are the same as those of the first embodiment.

In the illustrated example, the detection unit 21 includes an outlet position 21 (a) of the boiler 3 where SO _{3 in} the exhaust gas and the ammonia concentration before reaction can be measured, and the ammonia concentration of the remaining ammonia gas after the reaction with SO _3. Are arranged at the exit position 21 (b) of the economizer 4a, which is a measurable position.

Since the amount of SO _{X and the} like generated by the combustion of garbage varies depending on the nature of the waste, the furnace load, etc., it reacts with SO _{3 in} the exhaust gas depending on the amount of urea water sprayed from the urea water spray device 2A. There is a possibility that excessive ammonia gas may be generated. Ammonia gas that has not reacted with SO ₃ in the exhaust gas is contained in the fly ash repaired by the bag filter 6, and causes an irritating odor. Further, if ammonia is excessively contained in the exhaust gas, purple smoke is generated from the chimney.

At the outlet position 21 (a) of the boiler 3, the concentration of ammonia gas generated by spraying urea water is detected, and at the outlet position 21 (b) of the economizer 4a, the remaining ammonia gas is consumed by the neutralization reaction with SO _3. The concentration of is detected. From these detection results, the problem due to unreacted ammonia can be solved by calculating the required ammonia concentration according to the catalyst amount of the catalyst denitration tower 8 and controlling the injection amount of urea water.

  The ammonia gas concentration detection unit 21 may employ, for example, a semiconductor laser ammonia concentration meter, and the control unit 22 receives, for example, a detection value signal from the detection unit 21 and follows a control program recorded in advance. The urea water spray amount is calculated in the catalyst denitration tower 8 so that the necessary ammonia concentration is obtained, and the spray amount of the urea water spray device 2A is controlled by opening and closing the flow rate control means 2d such as a solenoid valve by PID control or the like. By doing so, generation | occurrence | production of purple smoke etc. can be prevented.

  The present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the said embodiment, although the waste incinerator 1 is a stalker type, it is not limited to this, The form, arrangement | positioning, etc. of the boiler 3 are not limited to the example of illustration.

  Further, the concentration meter of ammonia gas is not limited to the number and arrangement in the illustrated example. For example, the ammonia gas concentration meter can be provided only at the position 21 (a) without being provided at the position 21 (b), or the heater for the deaerator. It can also be provided immediately after 4b, immediately before or immediately after the catalyst denitration tower 8.

  Furthermore, although the example applied to the waste incineration facility is shown in the above embodiment, the present invention is not limited to this, and the present invention can be widely applied to apparatuses and methods for treating exhaust gas containing nitrogen oxides and / or sulfur oxides. For example, the present invention can be applied to treatment of exhaust gas discharged from a combustion furnace such as a gas combustion furnace attached to a gasification melting furnace, a furnace of a combustion boiler used for power generation, hot water use, or the like.

  In addition, as a facility for cooling the high-temperature exhaust gas discharged from the combustion furnace, other gas cooling facilities, for example, a known water jet cooling facility can be provided instead of the boiler or the low-temperature heat recovery device. When a boiler or a low-temperature heat recovery device is not provided, the ammonia concentration control by spraying urea water is performed by detecting the ammonia concentration by a detection unit disposed at a downstream position of the gas cooling facility, and the detected value of the catalyst denitration tower is determined in advance. The urea water injection amount can be controlled so that the ammonia concentration corresponds to the catalyst amount.

1 is a schematic view showing a waste incineration facility including a first embodiment of an exhaust gas treatment apparatus according to the present invention. It is the schematic which shows the waste incineration facility containing 2nd Embodiment of the waste gas processing apparatus which concerns on this invention. It is the schematic which shows the conventional refuse incineration facility.

Explanation of symbols

1 Combustion furnace (garbage incinerator)
2A Urea water spray device
3 Boiler 4 Low-temperature heat recovery device 6 Dust collection equipment (bug filter)
7 Reheater 8 Catalytic denitration tower 9 Induction ventilator 10 Chimney 11 Deaerator 12 Dry exhaust gas treatment device 13 Ammonia vaporizer 14 Ammonia storage tank

Claims (8)

A gas cooling facility for cooling the exhaust gas discharged from the combustion furnace, a urea water spraying device for spraying urea water onto the exhaust gas in the temperature range of 400 to 700 ° C., and the urea water being sprayed by the gas cooling facility An exhaust gas treatment apparatus comprising: a dust collection facility that collects dust in exhaust gas; and a catalyst denitration facility that performs catalyst denitration on exhaust gas from which dust has been removed by the dust collection facility. An exhaust heat boiler that recovers the heat of the exhaust gas discharged from the combustion furnace, a urea water spray device for spraying urea water to the exhaust gas in a temperature range of 400 to 700 ° C. by heat recovery by the exhaust heat boiler, An exhaust gas treatment apparatus comprising: a low-temperature heat recovery unit that recovers heat from a low-temperature exhaust gas sprayed with urea water while being heat-recovered by an exhaust heat boiler. It further comprises a dust collection facility for collecting dust in the exhaust gas heat recovered by the low-temperature heat recovery device, and a catalyst denitration facility for catalytic denitration of the exhaust gas from which dust has been removed by the dust collection facility. The exhaust gas treatment apparatus according to claim 2. A detection unit for detecting the ammonia gas concentration in the exhaust gas at a downstream position of the urea water spray device;
Based on the detection result of the detection unit, a control unit for controlling the spray amount of urea water by the urea water spray device;
The exhaust gas treatment apparatus according to claim 1, further comprising: The exhaust gas discharged from the combustion furnace and containing nitrogen oxides is cooled to 400 ° C to 700 ° C, urea gas is sprayed on the exhaust gas cooled to 400 to 700 ° C to generate ammonia gas, and the exhaust gas is generated by the generated ammonia gas. An exhaust gas treatment method comprising reducing the concentration of nitrogen oxides in exhaust gas by catalytic denitration. The exhaust gas discharged from the combustion furnace and containing sulfur oxides is cooled to 400 ° C. to 700 ° C., and urea gas is sprayed on the exhaust gas cooled to 400 to 700 ° C. to generate ammonia gas. An exhaust gas treatment method characterized in that sulfuric acid corrosion is prevented by neutralizing SO ₃ . The exhaust gas containing nitrogen oxides and sulfur oxides discharged from the combustion furnace is cooled to 400 ° C. to 700 ° C., urea gas is sprayed on the exhaust gas cooled to 400 to 700 ° C. to generate ammonia gas, and the generated ammonia Sulfuric acid corrosion is prevented by neutralizing SO ₃ in the exhaust gas with gas, and the concentration of nitrogen oxides in the exhaust gas is reduced by catalytic denitration of the exhaust gas with ammonia gas remaining without reacting with SO ₃ An exhaust gas treatment method characterized by the above. The ammonia gas concentration in the exhaust gas sprayed with urea water is detected, and the spray amount of urea water is controlled based on the detection result of the ammonia gas concentration. Exhaust gas treatment method.

Images